1. Technical Field
The present invention relates to an ink composition comprising a conductive polymer and, more particularly, to a conductive polymeric ink composition having controlled pH, wherein pH of the ink composition is adjusted to a desired neutral pH value while maintaining dispersibiltiy of PEDOT:PSS (Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) used as a main component of the ink composition, thereby solving problems due to strong acidity, including a reduction in the lifetime of devices, and also in which a transparent conductive polymer thin film formed from the ink composition has low haze, low resistance and high conductivity, compared to thin films manufactured conventionally.
2. Description of the Related Art
PEDOT:PSS (Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) is currently actively utilized in photoelectronic organic devices and so on because of high electrical conductivity and transparency thereof. In particular, PEDOT:PSS films may be applied to touch screens, organic light emitting diodes, and e-papers. To this end, conductivity thereof is required to increase using dimethyl sulfoxide, sorbitol, ionic liquids, and surfactants.
Also, PEDOT:PSS may be employed for a transparent electrode or a hole transport layer for OPV (Organic Photovoltaics), OLED (Organic Light Emitting Diode), etc. However, the use of PEDOT:PSS having strong acidity (pH 1˜2) may undesirably result in shortened lifetime of devices and corroded systems. To solve such problems, many attempts have been made to control the pH of PEDOT:PSS to a neutral pH value using a strong alkaline solution such as ammonia water or sodium hydroxide (NaOH). In this case, however, the dispersibility of PEDOT:PSS may deteriorate to thus remarkably decrease conductivity. Hence, there is a need for a method of adjusting the pH of PEDOT:PSS to a neutral pH value while maintaining the dispersibility of PEDOT:PSS.